The distribution of static strain along the fillet on an upper deck of cylinder block and its dependency on the depth of thread engagement for cylinder head bolts were evaluated for a diesel engine by the finite element method. Since the fillet on upper deck is one of the critical parts in the cylinder block that may be cracked by stress and strain concentration, the static strain along the fillet was focused on in this study. In the model, the static tightening force of cylinder head bolts balanced with the total force acting on the cylinder block. A uniform surface pressure calculated by the total force divided by the contact area was given to the upper deck. The following results were obtained.
The static strain along the fillet was dependent on the circumferential direction of cylinder and its value was varied with the depth of thread engagement for cylinder head bolts. The optimum depth of thread engagement was determined to be about 100 mm from the viewpoints of the overall magnitude of strain, the circumferential fluctuation of strain, the change rate of strain against the depth of thread engagement, and the length of cylinder head bolt. The calculated circumferential distribution of the static strain and the tightening force were compared with the measurement results under the optimum depth of thread engagement condition. Both results agreed well and this fact suggests that the present analysis is useful for optimizing the structural design of cylinder block for diesel engines.